This application claims the priority of Dutch application no. NL 1012127, filed May 21, 1999, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an assembly for desorbing sampling tubes.
2. Background of the Invention.
It is well known to store samples of gases, liquids or like fluids in so-called sampling tubes. To that end, see, for instance, EP-A-0 816 823, the disclosure of which is to be considered inserted herein. Also solid substance in the form of granules or the like is stored in sampling tubes. Often, but not always, such sampling tubes are filled with absorption material in which the gas or the liquid, at least the substances present therein, are absorbed. Such sampling tubes are used, for instance, in surroundings where the danger exists that the atmosphere becomes contaminated, as in, for instance, laboratories, chemical factories, submarines and the like. Thus there are sampling tubes where the air to be measured is actively pumped through the sampling tube and where the sampling tube is therefore provided with an inflow opening and an outflow opening. When a sample of a gas to be sampled is being taken, the gas is pumped into the inflow opening, and the gas leaves the sampling tube via the outflow opening while leaving the substances contained in the gas behind in the absorption material. This procedure of sampling is designated as active sampling. Also known, from practice, is so-called passive sampling. In that case the sampling tubes have only one inflow opening during sampling. The air or the gas to be sampled diffuses via that opening into the absorption material while leaving the substances contained in the gas behind in the absorption material.
After some time has passed after sampling, the sampling tube is desorbed. To that end, heretofore, use has been made of special devices which are particularly costly. Desorption of the sampling tube occurs by heating the sampling tube, so that the substances present in the absorption material or in the solid substance contained in the sampling tube evaporate and are liberated. By blowing a carrier gas through the sampling tube during heating, the liberated substances are entrained by the carrier gas and can, for instance, be temporarily collected in a cold trap and subsequently be passed from the cola trap to a gas chromatograph in which the gases released can be analyzed. The known desorption devices are therefore provided with carrier gas supply means, heating means, a cold trap, control means for controlling the heating means and the like. This has as a result that the known desorption devices have a considerable cost price, which are of the order of a few tens of thousands of guilders.
The invention envisages an entirely new type of assembly by means of which sampling tubes can be desorbed, and which has a much lower cost price. Essentially, the invention is based on the insight that the gas chromatograph, which is necessary anyhow, essentially has all the means that are also used in a known desorption device. By means of the assembly, these means already present in the gas chromatograph are made available for desorbing sampling tubes.
To that end, the invention provides an assembly for desorbing sampling tubes, the assembly comprising a gas chromatograph known per se provided with an injector, the sampling tubes having an inflow opening and an outflow opening, the assembly comprising an adapter which is placed in the injector and which is provided with a chamber which is bounded by a heat conducting housing, the adapter being arranged for placing a sampling tube in the chamber thereof, while in a condition where a sampling tube is placed in the Adapter, the inflow opening of the sampling tube is in fluid communication with a first carrier gas supply duct, while the outflow opening of the sampling tube is in fluid communication via the injector with a gas chromatography column contained in the gas chromatograph.
Due to the heat conducting housing of the adapter which bounds a chamber in which a sampling tube can be placed, it is possible by means of the heating means situated in the known injector of the known gas chromatograph, to heat a sampling tube placed in the chamber mentioned. Because moreover the inflow opening of the sampling tube is in fluid communication with a first carrier gas supply duct, and the outflow opening of the sampling tube is in fluid communication, via the injector, with a gas chromatography column contained in the gas chromatograph, substances located in the sampling tube that are liberated under the influence of the heating of the tube, can flow along with the carrier gas and be analyzed in the gas chromatography column. Since the known gas chromatograph has an extensive control by means of which the heating means of the injector can be accurately set, the temperature of the sampling tube contained in the chamber of the adapter can be accurately controlled, so that any particular temperature course of the sampling tube can be realized very accurately Thus, for instance, first the light fractions contained in the sampling tube can be released by heating the sampling tube to, for instance, 50xc2x0 C. for some time, whereafter subsequently heavier fractions can be liberated by heating the sampling tube to, for instance, 150xc2x0-250xc2x0 C.
According to a further elaboration, it is particularly favorable when the adapter is provided with a heat conducting tube which is connected with the heat conducting housing, such that the tube and the housing are in heat exchange with each other, while the tube of the adapter, in the fitted condition of the adapter, reaches into the injector chamber. Because the tube reaches into the injector chamber, the heat transfer from the heating means of the injector will occur much more efficiently in that the tube of the adapter is directly surrounded by the heating means of the injector.
According to a further elaboration of the invention, it is particularly favorable when the sampling tubes have the shape of a vial known per se. When, according to a further elaboration of the invention, the assembly further comprises an autosampler known per se, which autosampler comprises a setup rack in which a number of vial-shaped sampling tubes can be set up, while the manipulator of the autosampler is arranged for picking up a sampling tube from the setup rack and placing such sampling tube in the adapter.
With such a device, without intervention of a laboratory worker, a large number of sampling tubes can be desorbed. Normally, the autosampler known per se is used to spout a liquid sample contained in a vial from this vial into the injector. The manipulator of the autosampler moves the vial in question from the setup rack into what is designated in practice by the term turret, from where an automatically operable spout sucks up the sample from the vial and then injects it into the injector of the gas chromatograph. As a result of the fact that the sampling tubes have the same shape as a vial known per se, the autosampler in most cases already present can be used for converting the gas chromatograph to a sampling tube desorbing device.
The invention also relates to an adapter evidently intended for use in an assembly according to the invention. Further, the invention relates to a sampling tube evidently intended for use in an assembly according to the invention.
Furthermore, the invention relates to a kit of parts comprising at least one adapter according to the invention, as well as a support for mounting an autosampler known per se on a gas chromatograph known per se, the support being designed such that the autosampler can place the sampling tubes in the adapter, which is placed in an injector of the gas chromatograph, without requiring adjustment of the control of the autosampler. It is then preferred when the kit also comprises various carrier gas ducts, at least one T-piece and a valve assembly.